Glossary of Glacier Terminology

Glacier terms commonly utilized in the blog.

Ablation

The loss of ice and snow from a glacier system. This occurs through a variety of processes including melting and runoff, sublimation, evaporation, calving, and wind transportation of snow out of a glacier basin.

Accumulation

The addition of ice and snow into a glacier system. This occurs through a variety of processes including precipitation, firnification, and wind transportation of snow into a glacier basin from an adjacent area.

Accumulation Area

The part of a glacier that is perennially covered with snow. Also called Névé.

Advance

An increase in the length of a glacier compared to a previous point in time. As ice in a glacier is always moving forward, a glacier’s terminus advances when less ice is lost due to melting and/or calving than the amount of yearly advance.

Barren Zone

An area of fresh, vegetation-free bedrock around the margin of a retreating glacier that documents the recent loss of ice.

Braided Stream (Anastomizing Stream)

A stream that is characterized by a complex network of branches that continuously separate and reunite. Streams braid when they have a much greater sediment load than they can carry. Also called an Anastomosing Stream/.

 

Calving

The process by which pieces of ice break away from the terminus of a glacier that ends in a body of water or from the edge of a floating ice shelf that ends in the ocean. Once they enter the water, the pieces are called icebergs.

Chatter Marks

A series of small, closely spaced, crescentic grooves or scars formed in bedrock by rocks frozen in basal ice as they move along and chip the glacier’s bed. The horns of the crescent generally point down glacier.

Downwasting

The thinning of a glacier due to the melting of ice. This loss of thickness may occur in both moving and stagnant ice. Also called Thinning.

Drift

A collective term used to describe all types of glacier sedimentary deposits, regardless of the size or amount of sorting. The term includes all sediment that is transported by a glacier, whether it is deposited directly by a glacier or indirectly by running water that originates from a glacier.

Drumlin

An elongated ridge of glacial sediment sculpted by ice moving over the bed of a glacier. Generally, the down-glacier end is oval or rounded and the up-glacier end tapers. The shape is often compared to an inverted, blunt-ended canoe. Although not common in Alaska, drumlins cover parts of the Eastern and Midwestern United States (Irish).

Erratic

A rock of unspecified shape and size, transported a significant distance from its origin by a glacier or iceberg and deposited by melting of the ice. Erratics range from pebble-size to larger than a house and usually are of a different composition that the bedrock or sediment on which they are deposited.

Esker

A meandering, water-deposited, generally steep-sided sediment ridge that forms within a subglacial or englacial stream channel. Its floor can be bedrock, sediment, or ice. Subsequent melting of the glacier exposes the deposit. Generally composed of stratified sand and gravel, eskers can range from feet to miles in length and may exceed 100 feet in height.

Glacial Lake

An accumulation of standing liquid water on (supraglacial), in (englacial), or under (subglacial) a glacier.

Glacial Stream

A channelized accumulation of liquid water on (supraglacial), in (englacial), or under (subglacial) a glacier, moving under the influence of gravity.

Glacier

A large, perennial accumulation of ice, snow, rock, sediment and liquid water originating on land and moving down slope under the influence of its own weight and gravity; a dynamic river of ice. Glaciers are classified by their size, location, and thermal regime.

Glacier Cave

A cave formed in or under a glacier, typically by running water. Steam or high heat flow can also form glacier caves. Also called Ice Cave.

Glacier Flow

The movement of ice in a glacier, typically in a downward and outward direction, caused by the force of gravity. ‘Normal’ flow rates are in feet per day. ‘Rapid’ flow rates (i.e. surge) are in 10s or 100s of feet per day.

Glacier Ice

A mono-mineralic type of rock, composed of crystals of the mineral ice, formed through metamorphism of snowflakes. Metamorphism results in recrystallization, increased density, and the growth of hexagonal crystals. This ice comprises the majority of the mass of a glacier. Intermediate stages include Firn and Neve.

Ice-Dammed Lake

A lake that exists because its water is restricted from flowing by an ice dam. Sometimes these lakes form because an advancing glacier had blocked a valley.

Ice-Marginal Lake

A lake that is located adjacent to the terminus of a glacier. Typically, these lakes form in bedrock basins scoured by the glacier. They enlarge as the glacier retreats. Sometimes they are dammed by an End or Recessional Moraine.

Kame

A sand and gravel deposit formed by running water on stagnant or moving-glacier ice. Crevasse fills or crevasse ridges form within crevasses. Kames form on flat or inclined ice, in holes, or in cracks. A kame terrace forms between the glacier and the adjacent land surface. Shapes include hills, mounds, knobs, hummocks, or ridges.

Kettle

A depression that forms in an outwash plain or other glacial deposit by the melting of an in-situ block of glacier ice that was separated from the retreating glacier-margin and subsequently buried by glacier sedimentation. As the buried ice melts, the depression enlarges.

Mass Balance

A measure of the change in mass of a glacier at a certain point for a specific period of time. The balance between accumulation and ablation. Also called Mass Budget.

Moraine

A general term for unstratified and unsorted deposits of sediment that form through the direct action of, or contact with, glacier ice. Many different varieties are recognized on the basis of their position with respect to a glacier.

  • Ablation Moraine

An irregular-shaped layer or pile of glacier sediment formed by the melting of a block of stagnant ice. Ultimately, an ablation moraine is deposited on the former bed of the glacier. Also called Ablation Till.

  • Ground Moraine

A blanket of glacier till deposited on all of the surfaces over which a glacier moves, typically by moving ice.

  • Ice-cored Moraine

A moraine ridge consisting of a drape of sediment overlying a mass of stagnant ice.

  • Lateral Moraine

A sediment ridge, located on a glacier’s surface adjacent to the valley walls, extending down glacier to the terminus. It forms by the accumulation of rock material falling onto the glacier from the valley wall, rather than by water deposition.

  • Medial Moraine

A sediment ridge, located on a glacier’s exposed ice surface, away from its valley walls, extending down glacier to the terminus. It forms by the joining of two lateral moraines when two glaciers merge.

  • Push Moraine

A ridge or pile of unstratified glacial sediment that is formed in front of the ice margin by the terminus of an advancing glacier, bulldozing sediment in its path.

  • Recessional Moraine

A ridge of glacial sediment that forms when the terminus of a retreating glacier remains at or near a single location for a period of time sufficient for a cross-valley accumulation to form.

  • Terminal Moraine

A cross-valley, ridge-like accumulation of glacial sediment that forms at the farthest point reached by the terminus of an advancing glacier. Also called an End Moraine.

Moulin (Glacier Mill)

A narrow, tubular chute or crevasse through which water enters a glacier from the surface. Occasionally, the lower end of a moulin may be exposed in the face of a glacier or at the edge of a stagnant block of ice.

Outwash plain

A broad, low-slope angle alluvial plain composed of glacially eroded, sorted sediment (termed outwash), that has been transported by meltwater. The alluvial plain begins at the foot of a glacier and may extend for miles. Typically, the sediment becomes finer grained with increasing distance from the glacier terminus.

Pit Pond

A depression in an outwash plain by the melting of a block of ice floated to its depositional site by meltwater and subsequently buried by sediment. As it melts, a depression in the surface of the outwash plain develops.

Remnant

An isolated melting mass of glacier ice, that has become detached from its source and the remainder of the glacier. Some remnants cover many square miles.

Retreat

A decrease in the length of a glacier compared to a previous point in time. As ice in a glacier is always moving forward, its terminus retreats when more ice is lost at the terminus to melting and/or calving than reaches the terminus. During retreat, ice in a glacier does not move back up the valley.

Rock Flour

Fine-grained, silt-size sediment formed by the mechanical erosion of bedrock at the base and sides of a glacier by moving ice. When it enters a stream, it turns the stream’s color brown, gray, iridescent blue-green, or milky white. Also called Glacier Flour or Glacier Milk.

Stagnation

The in-situ melting of glacier ice. Many glaciers have stagnant termini, covered by thick sediment debris. Some support vegetation, including mature forests.

Striations

Multiple, generally parallel, linear grooves, carved by rocks frozen in the bed of a glacier into the bedrock over which it flows.

Surge

A short-lived, frequently large-scale, increase in the rate of movement of the ice within a glacier. Ice velocities may increase 10 to 100 times above normal flow rates. In some surges, the terminus of a glacier rapidly advances. Although not all glaciers surge, those that do often surge with some sort of a periodicity.

Terminus

The lower-most margin, end, or extremity of a glacier. Also called ToeEnd or Snout.

Till

An unsorted and unstratified accumulation of glacial sediment, deposited directly by glacier ice. Till is a heterogeneous mixture of different sized material deposited by moving ice (lodgement till) or by the melting in-place of stagnant ice (ablation till). After deposition, some tills are reworked by water.

Adapted from:  https://pubs.usgs.gov/of/2004/1216/text.html

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s